Parameter control in transport refrigeration system and methods for same

ABSTRACT

Embodiments of transport refrigeration systems, apparatus, and/or methods for the same can provide exemplary verification for operating characteristics thereof. In one embodiment, a calculated compressor mid stage pressure can be verified using a prescribed relationship to other transport refrigeration system characteristics.

CROSS-REFERENCE TO RELATED APPLICATION

Reference is made to and this application claims priority from and thebenefit of U.S. Provisional Application Ser. No. 61/254,280, filed Oct.23, 2009, and entitled PARAMETER CONTROL IN TRANSPORT REFRIGERATIONSYSTEM AND METHODS FOR SAME, which application is incorporated herein inits entirety by reference.

TECHNICAL FIELD

This invention relates generally to transport refrigeration systems andmethods for same and, more particularly, to methods and apparatus forcontrolling vapor compression systems.

BACKGROUND OF THE INVENTION

A particular difficulty of transporting perishable items is that suchitems must be maintained within a temperature range to reduce orprevent, depending on the items, spoilage or conversely damage fromfreezing. A transport refrigeration unit is used to maintain propertemperatures within a transport cargo space. The transport refrigerationunit can be under the direction of a controller. The controller ensuresthat the transport refrigeration unit maintains a certain environment(e.g. thermal environment) within the transport cargo space. Thecontroller can operate a transport refrigeration system and/orcomponents thereof responsive to sensors disposed in the system.

A vapor compression system can include a compressor, a heat rejectionheat exchanger (e.g., condenser or gas cooler), an expansion device, andan evaporator. Economizer cycles are sometimes employed to increase theefficiency and/or capacity of the system. Economizer cycles operate byexpanding the refrigerant leaving the heat rejecting heat exchanger toan intermediate pressure and separating the refrigerant flow into twostreams. One stream is sent to the heat absorbing heat exchanger, andthe other is sent to cool the flow between two compression stages. Inone form of an economizer cycle, a flash tank is used to perform theseparation. In an economizer cycle with flash tank, a refrigerantdischarged from the gas cooler passes through a first expansion device,and its pressure is reduced. Refrigerant collects in the flash tank aspart liquid and part vapor. The vapor refrigerant is used to coolrefrigerant exhaust as it exits a first compression device, and theliquid refrigerant is further expanded by a second expansion devicebefore entering the evaporator. Such a flash tank economizer isparticularly useful when operating in transcritical conditions, such asare required when carbon dioxide is used as the working fluid.

Due to the thermophysical properties of CO₂, the refrigeration systemcan operate in both the subcritical and transcritical modes. Thesubcritical mode is similar to the operation of systems withconventional refrigerants. In the transcritical mode the refrigerantpressure in the heat rejection heat exchanger, and possibly in the flashtank, is above the critical pressure, while the evaporator operates asin the subcritical mode.

DISCLOSURE OF THE INVENTION

In view of the background, it is an aspect of the application to providea transport refrigeration system, transport refrigeration unit, andmethods of operating the same that can maintain cargo quality byselectively controlling transport refrigeration system components.

One embodiment according to the application can include a control modulefor a transport refrigeration system. The control module includes acontroller for controlling the transport refrigeration system toselectively verify operations of components thereof.

In accordance with one aspect of the invention, operations of componentsof a transport refrigeration system can be directly measured (e.g.,sensors) and/or indirectly verified (e.g., without sensors).

In accordance with one aspect of the invention, an economizer includes acontrol for controlling operations of the economizer responsive topressure in a compressor.

In accordance with an aspect of the application, there is provided arefrigerant vapor compression system that can include a refrigerantcompression device to include a first compression stage and a secondcompression stage, a refrigerant heat rejection heat exchangerdownstream of the compression device, a refrigerant heat absorption heatexchanger downstream of the refrigerant heat rejection heat exchanger, afirst expansion device disposed downstream of the refrigerant heatrejection heat exchanger and upstream of the refrigerant heat absorptionheat exchanger, a sensor coupled to an output of the heat rejection heatexchanger, the sensor to measure a refrigerant temperature, and acontroller to control operation of the refrigeration vapor compressionsystem, the controller operative to indirectly verify the measuredrefrigerant temperature.

In accordance with an aspect of the application, there is provided acomputer program product comprising a computer usable storage medium tostore a computer readable program that, when executed on a computer,causes the computer to perform operations to operate a transportrefrigeration unit, the operations that can include operating thetransport refrigeration unit in a mode where a refrigerant iscirculating within a refrigerant circuit, sensing a characteristic usedto determine a system capacity of the transport refrigeration unitduring operation, indirectly determining the characteristic used todetermine the system capacity, comparing the sensed value of thecharacteristic used to determine the system capacity against theindirectly determined value, and determining an error condition of acorresponding sensor when a result of the comparison does not match.

In accordance with an aspect of the application, there is provided amethod for determining a characteristic of a refrigerant vaporcompression system having a refrigerant circuit including a refrigerantcompression device, a refrigerant heat rejection heat exchangerdownstream of the compression device, a refrigerant heat absorption heatexchanger downstream of the refrigerant heat rejection heat exchanger, asensor to sense a characteristic used to determine a system capacity ofthe refrigerant vapor compression system and interconnecting refrigerantlines as active components, the method that can include operating therefrigerant vapor compression system in a mode where the refrigerant iscirculating within the active components of the refrigerant circuit,indirectly determining the characteristic used to determine the systemcapacity, comparing the sensed value of the characteristic used todetermine the system capacity against the indirectly determined value ofthe characteristic, and determining an error condition of acorresponding sensor when a result of the comparison does not match.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram that shows an embodiment of a transportrefrigeration system according to the application;

FIG. 2 is a diagram that shows another embodiment of a transportrefrigeration system according to the application;

FIG. 3 is a schematic illustration of an embodiment of a vaporcompression system according to the application;

FIG. 4 is a diagram graphically showing exemplary refrigeranttemperature exiting a heat rejection heat exchanger as a function ofsystem capacity;

FIG. 5 is a diagram graphically showing exemplary compressor mid-stagepressure as a function of compressor discharge pressure for variouscompressor suction pressures according to embodiments of theapplication; and

FIG. 6 is a flow diagram showing an embodiment of a method for operatinga transport refrigeration system according to the application.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Reference will now be made in detail to exemplary embodiments of theapplication, examples of which are illustrated in the accompanyingdrawings. Whenever possible, the same reference numerals will be usedthroughout the drawings to refer to the same or like parts.

FIG. 1 is a diagram that shows an embodiment of a transportrefrigeration system. As shown in FIG. 1, transport refrigeration system100 can include a transport refrigeration unit 10 coupled to an enclosedspace within a container 12. The transport refrigeration system 100 maybe of the type commonly employed on refrigerated trailers. As shown inFIG. 1, the transport refrigeration unit 10 is configured to maintain aprescribed thermal environment within the container 12 (e.g., cargo inan enclosed volume).

In FIG. 1, the transport refrigeration unit 10 is connected at one endof the container 12. Alternatively, the transport refrigeration unit 10can be coupled to a prescribed position on a side or more than one sideof the container 12. In one embodiment, a plurality of transportrefrigeration units can be coupled to a single container 12.Alternatively, a single transport refrigeration unit 10 can be coupledto a plurality of containers 12 or multiple enclosed spaces within asingle container. The transport refrigeration unit 10 can operate toinduct air at a first temperature and to exhaust air at a secondtemperature. In one embodiment, the exhaust air from the transportrefrigeration unit 10 will be warmer than the inducted air such that thetransport refrigeration unit 10 is employed to warm the air in thecontainer 12. In one embodiment, the exhaust air from the transportrefrigeration unit 10 will be cooler than the inducted air such that thetransport refrigeration unit 10 is employed to cool the air in thecontainer 12. The transport refrigeration unit 10 can induct air fromthe container 12 having a return temperature Tr (e.g., firsttemperature) and exhaust air to the container 12 having a supplytemperature Ts (e.g., second temperature).

In one embodiment, the transport refrigeration unit 10 can include oneor more temperature sensors to continuously or repeatedly monitor thereturn temperature Tr and/or the supply temperature Ts. As shown in FIG.1, a first temperature sensor 24 of the transport refrigeration unit 10can provide the supply temperature Ts and a second temperature sensor 22of the transport refrigeration unit 10 can provide the returntemperature Tr to the transport refrigeration unit 10, respectively.Alternatively, the supply temperature Ts and the return temperature Trcan be determined using remote sensors.

A transport refrigeration system 100 can provide air with controlledtemperature, humidity or/and species concentration into an enclosedchamber where cargo is stored such as in container 12. As known to oneskilled in the art, the transport refrigeration system 100 (e.g.,controller 250) is capable of controlling a plurality of theenvironmental parameters or all the environmental parameters withincorresponding ranges with a great deal of variety of cargos and underall types of ambient conditions.

FIG. 2 is a diagram that shows an embodiment of a transportrefrigeration system. As shown in FIG. 2, a transport refrigerationsystem 200 can include a transport refrigeration unit 210 coupled to acontainer 212, which can be used with a trailer, an intermodalcontainer, a train railcar, a ship or the like, used for thetransportation or storage of goods requiring a temperature controlledenvironment, such as, for example foodstuffs and medicines (e.g.,perishable or frozen). The container 212 can include an enclosed volume214 for the transport/storage of such goods. The enclosed volume 214 maybe an enclosed space having an interior atmosphere isolated from theoutside (e.g., ambient atmosphere or conditions) of the container 212.

The transport refrigeration unit 210 is located so as to maintain thetemperature of the enclosed volume 214 of the container 212 within apredefined temperature range. In one embodiment, the transportrefrigeration unit 210 can include a compressor 218, a condenser heatexchanger unit 222, a condenser fan 224, an evaporation heat exchangerunit 226, an evaporation fan 228, and a controller 250. Alternatively,the condenser 222 can be implemented as a gas cooler.

The compressor 218 can be powered by single phase electric power, threephase electrical power, and/or a diesel engine and can, for example,operate at a constant speed. The compressor 218 may be a scrollcompressor, a rotary compressor, a reciprocal compressor, or the like.The transport refrigeration system 200 requires electrical power from,and can be connected to a power supply unit (not shown) such as astandard commercial power service, an external power generation system(e.g., shipboard), a generator (e.g., diesel generator), or the like.

The condenser heat exchanger unit 222 can be operatively coupled to adischarge port of the compressor 218. The evaporator heat exchanger unit226 can be operatively coupled to an input port of the compressor 218.An expansion valve 230 can be connected between an output of thecondenser heat exchanger unit 222 and an input of the evaporator heatexchanger unit 226.

The condenser fan 224 can be positioned to direct an air stream onto thecondenser heat exchanger unit 222. The air stream from the condenser fan224 can allow heat to be removed from the coolant circulating within thecondenser heat exchanger unit 222.

The evaporator fan 228 can be positioned to direct an air stream ontothe evaporation heat exchanger unit 226. The evaporator fan 228 can belocated and ducted so as to circulate the air contained within theenclosed volume 214 of the container 212. In one embodiment, theevaporator fan 230 can direct the stream of air across the surface ofthe evaporator heat exchanger unit 226. Heat can thereby be removed fromthe air, and the reduced temperature air can be circulated within theenclosed volume 214 of the container 212 to lower the temperature of theenclosed volume 214.

The controller 250 such as, for example, a MicroLink™ 2i or Advancedcontroller, can be electrically connected to the compressor 218, thecondenser fan 224, and/or the evaporator fan 228. The controller 250 canbe configured to operate the transport refrigeration unit 210 tomaintain a predetermined environment (e.g., thermal environment) withinthe enclosed volume 214 of the container 212. The controller 250 canmaintain the predetermined environment by selectively controllingoperations of the condenser fan 224, and/or the evaporator fan 228 tooperate at a low speed or a high speed. For example, if increasedcooling of the enclosed volume 214 is required, the controller 250 canincrease electrical power to the compressor 218, the condenser fan 224,and the evaporator fan 228. In one embodiment, an economy mode ofoperation of the transport refrigeration unit 210 can be controlled bythe controller 250. In another embodiment, variable speeds of componentsof the transport refrigeration unit 210 can be adjusted by thecontroller 250. In another embodiment, a full cooling mode forcomponents of the transport refrigeration unit 210 can be controlled bythe controller 250. In one embodiment, the electronic controller 250 canadjust a flow of coolant supplied to the compressor 218.

FIG. 3 is a diagram that shows an embodiment of a vapor compressionsystem according to the application. As shown in FIG. 3, an exemplaryembodiment of a refrigerant vapor compression system 300 designed foroperation in a transcritical cycle with a low critical pointrefrigerant, such as for example, but not limited to, carbon dioxide andrefrigerant mixtures containing carbon dioxide. However, it is to beunderstood that the refrigerant vapor compression system 300 may also beoperated in a subcritical cycle with a higher critical point refrigerantsuch as conventional hydrochlorofluorocarbon and hydrofluorocarbonrefrigerants.

The refrigerant vapor compression system 300 is particularly suitablefor use in a transport refrigeration system for refrigerating the air orother gaseous atmosphere within the temperature controlled enclosedvolume 214 such as a cargo space of a truck, trailer, container, or thelike for transporting perishable/frozen goods. The refrigerant vaporcompression system 300 is also suitable for use in conditioning air tobe supplied to a climate controlled comfort zone within a residence,office building, hospital, school, restaurant or other facility. Therefrigerant vapor compression system could also be employed inrefrigerating air supplied to display cases, merchandisers, freezercabinets, cold rooms or other perishable/frozen product storage areas incommercial establishments.

The refrigerant vapor compression system 300 includes a multi-stagecompression device 320, a refrigerant heat rejection heat exchanger 330,a refrigerant heat absorption heat exchanger 350, also referred toherein as an evaporator, and a primary expansion valve 355, such as forexample an electronic expansion valve as depicted in FIG. 3, operativelyassociated with the evaporators 350, with refrigerant lines 302, 304,and 306 connecting the aforementioned components in a primaryrefrigerant circuit. As depicted in FIG. 3, the refrigerant vaporcompression system 300 may also include an unload bypass line 316 thatestablishes refrigerant flow communication between an intermediatepressure stage of the multi-stage compression device 320 and the suctionpressure portion of the refrigerant circuit, which constitutesrefrigerant line 306 extending from the outlet of the evaporator 350 tothe inlet of the compression device 320.

Additionally, the refrigerant vapor compression system 300 can includean economizer circuit having an economizer device 340, a secondaryexpansion valve 345 and a refrigerant vapor injection line 314. As shownin FIG. 3, the economizer circuit includes a flash tank economizer 340interdisposed in refrigerant line 304 of the primary refrigerant circuitdownstream with respect to refrigerant flow of the refrigerant heatrejection heat exchanger 330 and upstream with respect to refrigerantflow of the refrigerant heat absorption heat exchanger 350. Thesecondary expansion device 345 is interdisposed in refrigerant line 304in operative association with and upstream of the economizer Thesecondary expansion device 345 may be an expansion valve, such as a highpressure electronic expansion valve as depicted in FIG. 3. Refrigeranttraversing the secondary expansion device 345 is expanded to a lowerpressure sufficient to establish a mixture of refrigerant in a vaporstate and refrigerant in a liquid state. The flash tank economizer 340includes a separation chamber 342 wherein refrigerant in the liquidstate collects in a lower portion of the separation chamber 342 andrefrigerant in the vapor state collects in the portion of the separationchamber 342 above the liquid refrigerant.

The refrigerant vapor injection line 314 establishes refrigerant flowcommunication between an upper portion of the separation chamber 342 ofthe flash tank economizer 340 and an intermediate stage of thecompression process. A vapor injection flow control device 343 isinterdisposed in vapor injection line 314. The vapor injection flowcontrol device 343 may comprise a flow control valve selectivelypositionable between an open position where refrigerant vapor flow maypass through the refrigerant vapor injection line 314 and a closedposition where refrigerant vapor flow through the refrigerant vaporinjection line 314 is reduced or blocked. In one embodiment, the vaporinjection flow control valve 343 comprises a two-position solenoid valveof the type selectively positionable between a first open position and asecond closed position.

The refrigeration vapor compression system 300 can also include anoptional variable flow device (VFD) or a suction modulation valve (SMV)323 interdisposed in refrigerant line 306 at a location between theoutlet of the refrigeration heat absorption heat exchanger 350 and aninlet to the compression device 320. In the exemplary embodimentdepicted in FIG. 3, the suction modulation valve 323 is positioned inrefrigerant line 306 between the outlet of the evaporator 350 and thepoint at which the compressor unload bypass line 316 intersectsrefrigerant line 306. In one embodiment, the suction modulation valve323 may comprise a pulse width modulated solenoid valve.

In a refrigerant vapor compression system operating in a transcriticalcycle, the refrigerant heat rejection heat exchanger 330 constitutes agas (refrigerant vapor) cooler through which supercritical refrigerantpasses in heat exchange relationship with a cooling medium, such as forexample, but not limited to ambient gas or liquid (e.g., air or water),and may be also referred to herein as a gas cooler. In a refrigerantvapor compression system operating in a subcritical cycle, therefrigerant heat rejection heat exchanger 330 can constitute arefrigerant condensing heat exchanger through which hot, high pressurerefrigerant vapor passes in heat exchange relationship with the coolingmedium and is condensed to a liquid. As shown in FIG. 3, the refrigerantheat rejection heat exchanger 330 includes a finned tube heat exchanger332, such as for example a fin and round tube heat exchange coil or afin and mini-channel flat tube heat exchanger, through which therefrigerant passes in heat exchange relationship with ambient air beingdrawn through the finned tube heat exchanger 332 by the fan(s) 334associated with an exemplary gas cooler 330.

Whether the refrigerant vapor compression system 300 is operating in atranscritical cycle or a subcritical cycle, the refrigerant heatabsorption heat exchanger 350 serves an evaporator wherein refrigerantliquid or a mixture of refrigerant liquid and vapor is passed in heatexchange relationship with a fluid to be cooled, most commonly air,drawn from and to be returned to a temperature controlled environment,such as a cargo box of a refrigerated transport truck, trailer orcontainer, or a display case, merchandiser, freezer cabinet, cold roomor other perishable/frozen product storage area in a commercialestablishment, or to a climate controlled comfort zone within aresidence, office building, hospital, school, restaurant or otherfacility. As shown in FIG. 3 the refrigerant heat absorption heatexchanger 350 comprises a finned tube heat exchanger 352 through whichrefrigerant passes in heat exchange relationship with air drawn from andreturned to the refrigerated container 212 by the evaporator fan(s) 354associated with the evaporator 350. The finned tube heat exchanger 352may comprise, for example, a fin and round tube heat exchange coil or afin and mini-channel flat tube heat exchanger.

The compression device 320 functions to compress the refrigerant and tocirculate refrigerant through the primary refrigerant circuit asdescribed in detail herein. In the embodiment depicted in FIG. 3, thecompression device 320 may comprise a single multiple stage refrigerantcompressor, such as for example a screw compressor or a reciprocatingcompressor disposed in the primary refrigerant circuit and having afirst compression stage 320 a and a second compression stage 320 b. Thefirst and second compression stages are disposed in series refrigerantflow relationship with the refrigerant leaving the first compressionstage 320 a passing directly to the second compression stage 320 b forfurther compression. Alternatively, the compression device 320 maycomprise a pair of independent compressors 320 a and 320 b, connected inseries refrigerant flow relationship in the primary refrigerant circuitvia a refrigerant line connecting the discharge outlet port of the firstcompressor 320 a in refrigerant flow communication with an inlet port(e.g. the suction inlet port) of the second compressor 320 b. In theindependent compressor embodiment, the compressors 320 a and 320 b maybe scroll compressors, screw compressors, reciprocating compressors,rotary compressors or any other type of compressor or a combination ofany such compressors. In the embodiment depicted in FIG. 3, therefrigerant vapor compression system 300 includes a refrigerant bypassline 316 providing a refrigerant flow passage from an intermediatepressure stage of the compression device 320 back to the suction side ofthe compression device 320. An unload valve 327 is interdisposed in thebypass line 316. The unload valve 327 may be selectively positioned inan open position in which refrigerant flow passes through the bypassline 316 and a closed position in which refrigerant flow through thebypass line 316 is reduced or blocked.

In the embodiment depicted in FIG. 3, the refrigerant vapor compressionsystem 300 further includes a refrigerant liquid injection line 318. Therefrigerant liquid injection line 318 can tap into refrigerant line 304at location downstream of the flash tank economizer 340 and upstream ofthe primary expansion valve 355 and open into an intermediate stage ofthe compression process. Thus, the refrigerant liquid injection line 318can establish refrigerant flow communication between a lower portion ofthe separation chamber 342 of the flash tank economizer 340 and anintermediate pressure stage of the compression device 320. In oneembodiment, the refrigerant liquid injection line 318 can establishrefrigerant flow communication between a lower portion of the separationchamber 342 of the flash tank economizer 340 and a compressor suctionline (e.g., an inlet to the compression device). A liquid injection flowcontrol device 353 can be interdisposed in refrigerant liquid injectionline 318. The liquid injection flow control device 353 may comprise aflow control valve selectively positionable between an open positionwherein refrigerant liquid flow may pass through the liquid injectionline 318 and a closed position wherein refrigerant liquid flow throughthe refrigerant liquid injection line 318 is reduced or blocked. In anembodiment, the liquid injection flow control device 353 comprises atwo-position solenoid valve of the type selectively positionable betweena first open position and a second closed position.

In the exemplary embodiment of the refrigerant vapor compression system300 depicted in FIG. 3, injection of refrigerant vapor or refrigerationliquid into the intermediate pressure stage of the compression processwould be accomplished by injection of the refrigerant vapor orrefrigerant liquid into the refrigerant passing from the firstcompression stage 320 a into the second compression stage 320 b of thecompression device 320.

Liquid refrigerant collecting in the lower portion of the flash tankeconomizer 340 can pass therefrom through refrigerant line 304 andtraverse the primary refrigerant circuit expansion valve 355interdisposed in refrigerant line 304 upstream with respect torefrigerant flow of the evaporator 350. As this liquid refrigeranttraverses the first expansion device 355, it expands to a lower pressureand temperature before entering the evaporator 350. The evaporator 350constitutes a refrigerant evaporating heat exchanger through whichexpanded refrigerant passes in heat exchange relationship with the airto be cooled, whereby the refrigerant is vaporized and typicallysuperheated. As in conventional practice, the primary expansion valve355 meters the refrigerant flow through the refrigerant line 304 tomaintain a desired level of superheat in the refrigerant vapor leavingthe evaporator 350 to ensure that no liquid is present in therefrigerant leaving the evaporator. The low pressure refrigerant vaporleaving the evaporator 350 returns through refrigerant line 306 to theinput port of the first compression stage or first compressor 320 a ofthe compression device 320 in the embodiment depicted in FIG. 3.

The refrigerant vapor compression system 300 also includes a controlsystem operatively associated therewith for controlling operation of therefrigerant vapor compression system 300. The control system can includea controller 390 that can determine the desired mode of operation inwhich to operate the refrigerant vapor compression system 300 based uponconsideration of refrigeration load requirements, ambient conditions andvarious sensed system operating parameters. As shown in FIG. 3, thecontroller 390 also includes various sensors operatively associated withthe controller 390 and disposed at selected locations throughout thesystem for monitoring various operating parameters by use of varioussensors operatively associated with the controller. The control systemmay include, by way of example but not limitation, a pressure sensor 392disposed in operative association with the flash tank economizer 340 tosense the pressure within the separation chamber 342, a temperaturesensor 393 and a pressure sensor 394 for sensing the refrigerant inletor suction temperature and pressure, respectively, and a temperaturesensor 395 and a pressure sensor 396 for sensing refrigerant dischargetemperature and pressure, respectively. In transport refrigerationapplications, the refrigeration vapor compression system may alsoinclude a temperature sensor 397 a for sensing the temperature of theair returning to the evaporator from the container 212 and a temperaturesensor 397 b for sensing a temperature of the air being supplied to thecontainer 212. Sensors (not shown) may also be provided for monitoringambient outdoor conditions, such as or example ambient outdoor airtemperature and humidity. By way of example but not limitation; thepressure sensors 392, 394, 396 may be conventional pressure sensors,such as for example, pressure transducers, and the temperature sensors393, 395 may be conventional temperature sensors, such as for example,thermocouples or thermistors.

The controller 390 processes the data received from the various sensorsand controls operation of the compression device 320, operation of thefan(s) 334 associated with the refrigerant heat rejection heat exchanger330, operation of the fan(s) 354 associated with the evaporator 350,operation of the primary expansion device 355, operation of thesecondary expansion device 345, and operation of the suction modulationvalve 323. The controller 390 also controls the positioning of the vaporinjection valve 343 and liquid injection valve 353. The controller 390positions the vapor injection valve 343 in an open position forselectively permitting refrigerant vapor to pass from the flash tankeconomizer 340 through refrigerant vapor injection line 314 forinjection into an intermediate stage of the compression process.Similarly, the controller 390 positions the liquid injection valve 353in an open position for selectively permitting refrigerant liquid topass from the flash tank economizer 340 through refrigerant liquidinjection line 318 for injection into an intermediate pressure stage ofthe compression process. In the FIG. 3 embodiment, the controller 390can also control the positioning of the unload valve 327 to selectivelyopen the unload valve 327 to bypass refrigerant from an intermediatepressure stage of the compression device 320 through bypass line 316back to the suction side of the compression device 320 when it isdesired to unload the first stage of the compression device 320.

According to embodiments of the application, there are selectedoperation characteristics in a transport refrigeration system that canaffect performance or overall system performance. During transportrefrigeration system operations, it is desirable to check suchcharacteristics to determine proper component or system functions and/oroperations. In one embodiment, a measured value and a calculated valuefor a component/system performance characteristic can be determined andcompared, and then a judgment can be made responsive to or based on thecomparison.

For example, a compressor mid-stage pressure and gas cooler exittemperature can be used to control or optimize CO₂ economizedrefrigeration system operations for capacity and/or efficiency. In oneembodiment, gas cooler exit temperature is used to determine aprescribed compressor discharge pressure. In an embodiment, compressormid-stage pressure is used to determine whether economized mode can/isentered by a vapor compression system.

In a refrigeration system, the refrigerant temperature exiting the heatrejection heat exchanger reflects the heat exchanger coil and fanperformance. When the transport refrigeration system operates in atranscritical application, then the refrigerant temperature exiting theheat rejection heat exchanger is in the function that can determine oroptimize compressor discharge pressure in the refrigeration system foreither higher cooling capacity or higher energy efficiency. For at leastthis reason, embodiments of the application can determine or verify thatthis performance characteristic (e.g., refrigerant temperature exitingthe gas cooler) is within a prescribed range or a system design range.In one embodiment, the heat rejection heat exchanger is sized for thehighest capacity conditions of the system 300 (e.g., under which thesystem can be intended to operate). Therefore, for a majority or almostall of designed operating conditions, the heat rejection heat exchangeris oversized. As determined by the inventors, the refrigeranttemperature exiting heat rejection heat exchanger (e.g., shown as GCXTin the graph in FIG. 4) was determined (e.g., tested) to be onlyslightly higher than ambient temperature. Thus, in one embodiment, theexiting temperature of refrigerant for the heat rejection heat exchangercan be calculated or verified using ambient temperature plus a variableoffset. The variable offset can be determined to have a prescribedrelationship to the cooling capacity of the system 300. In oneembodiment, the highest offset can occur at highest cooling capacityconditions. As shown in FIG. 4, an offset is shown on the Y axis and canbe defined as (Tamb-GCXT). The temperature difference between evaporatorreturn air temperature (RTS) and supply air temperature (STS) is shownon X axis. The temperature difference (RTS-STS) is one exemplarymeasurement of system 300 cooling capacity. In one embodiment, thetemperature difference (RTS-STS) is directly related (e.g., a prescribedrelationship) to the transport refrigeration system cooling capacity.

In one embodiment, the transport refrigeration system capacity can bedetermined responsive to an operating mode of the transportrefrigeration system.

A sensor 382 can be provided in the system 300 shown in FIG. 3 tomeasure the refrigerant temperature exiting heat rejection heatexchanger 330. The sensor 382 can be a temperature sensor.Alternatively, the sensor 382 can be a pressure sensor where thetemperature can be determined using the pressure. In one embodiment, acalculated temperature can be compared to the temperature provided usingthe sensor 382. When corresponding values do not match, an errorcondition in the sensor 382 can be identified by the controller 390provided to an operator or the like.

In an economized refrigeration system, compressor mid stage pressure isan operation characteristic that can be monitored because the compressormid stage pressure affects whether the system can transition intoeconomized mode for higher capacity and higher energy efficiency. For atleast this reason, the controller 390 can operate to verify propercompressor functions determined through a compressor mid stage pressureperformance check during system 300 operations which can be executedaccording to embodiments of the application by a comparison of ameasured value and a calculated (e.g., indirect) value for thecompressor mid-stage pressure.

An exemplary indirect determination for the compressor mid-stagepressure will now be described. FIG. 5 shows the compressor mid-stagepressure as a function of the compressor discharge pressure for variouscompressor suction pressures. As shown in FIG. 5, the compressormid-stage pressure can be determined when the suction and dischargepressure of the compressor 320 are known. The same information can bewritten in the form of an exemplary two-dimensional lookup table below.

P Suction 1 P Suction 2 P Suction 3 P Suction 4 P Discharge 1 PMid-Stage 1, 1 P Mid-Stage 1, 2 P Mid-Stage 1, 3 P Mid-Stage 1, 4 PDischarge 2 P Mid-Stage 2, 1 P Mid-Stage 2, 2 P Mid-Stage 2, 3 PMid-Stage 2, 4 P Discharge 3 P Mid-Stage 3, 1 P Mid-Stage 3, 2 PMid-Stage 3, 3 P Mid-Stage 3, 4 P Discharge 4 P Mid-Stage 4, 1 PMid-Stage 4, 2 P Mid-Stage 4, 3 P Mid-Stage 4, 4

It should be understood that the values of the suction, discharge, andmid-stage pressures are specific to the compressor design and operatingconditions (e.g., compressor 320). When the operating conditions for agiven compressor machine change, for instance if the suction superheatchanges, the values of the mid-stage pressure for a particularcombination of suction and discharge pressure may change. This can bemore pronounced if the compressor design allows to independently controlthe speed of the two compressor stages, for instance if the two stagesare driven by different motors, for which the speed can be adjustedindependently from each other. In this case, an additional dimension canbe added to the graph or lookup table. For example, an additionaldimension can be accomplished by providing additional graphs or tables,each for a constant value of the additional variable.

A sensor 384 can be provided in the system 300 shown in FIG. 3 tomeasure the compressor mid-stage pressure. The sensor 384 can be apressure sensor. In one embodiment, a calculated compressor mid-stagepressure can be compared to the compressor mid-stage pressure providedusing the sensor 384. When corresponding values do not match, an errorcondition in the sensor 384 can be determined by the controller 390provided to an operator or the like.

An embodiment of a method of operating a transport refrigeration unitaccording to the application will now be described. The methodembodiment shown in FIG. 6, can be implemented in and will be describedusing a refrigerant vapor compression system embodiment shown in FIG. 3,however, the method embodiment is not intended to be limited thereby.

Referring now to FIG. 6, a process as performed by the controller 390can be shown in block diagram form. After a process starts during systemoperations, an operating characteristic of the system can be measured(e.g., Cm) (operation block 610). Then, the operating characteristic ofthe system can be indirectly determined or calculated (e.g., Cc) fromother system components and/or characteristics according to a prescribedrelationship (operation block 620). It can be determined whether Cm andCc match (operation block 630). When the determination in operationblock 630 is negative, an error condition can be processed (operationblock 640). When the determination in operation block 630 is affirmativeor from operation block 640, a delay period (operations block 650) canbe processed before control returns to operation block 610.

In one embodiment, a calculated measurement for a system characteristiccan be more accurate than a measured value. Thus, the error conditioncan be processed in operation block 640 by having the controller 390stop using the measure value Cm and begin using the calculated value Cc.

In one embodiment, a calculated or indirect measurement of selectedcharacteristics (e.g., compressor unit stage pressure and/or gas coolerrefrigerant exit temperature) of transport refrigeration systemsincluding refrigerant vapor compression systems can be determined withsufficient accuracy that sensors can be reduced or eliminated from thesystem, which may increase reliability and decrease size and cost. Inone embodiment, the controller 390 can be responsive to a pressuredifference between the flash tank and a mid-stage of the compressor toprotect or prevent operation of the economizer during periods in whichthe pressure at the mid-stage is greater than the pressure in the flashtank or control operations of a flow control device (e.g., flow controldevice 343, 353) coupled thereto.

Embodiments according to the application can use remote sensors torespectively measure an environment within the container 12 such as thereturn air temperature RTS and the supply air temperature STS. Remotesensors, as known to one skilled in the art, can communicate with acontroller (e.g., transport refrigeration unit 10) through wire orwireless communications. For example, wireless communications caninclude one or more radio transceivers such as one or more of 802.11radio transceiver, Bluetooth radio transceiver, GSM/GPS radiotransceiver or WIMAX (802.16) radio transceiver. Information collectedby remote sensor(s) can be used as input parameters for a controller tocontrol various components in transport refrigeration systems. In oneembodiment, remote sensors may monitor additional criteria such ashumidity, species concentration or the like.

It should be recognized that selected procedures described herein mayresult in some liquid refrigerant entering the compressor inlet.Although this is generally undesirable, it may occur for short periodsof time without any significant damage to the compressor.

While the present invention has been described with reference to anumber of specific embodiments, it will be understood that the truespirit and scope of the invention should be determined only with respectto claims that can be supported by the present specification. Further,while in numerous cases herein wherein systems and apparatuses andmethods are described as having a certain number of elements it will beunderstood that such systems, apparatuses and methods can be practicedwith fewer than the mentioned certain number of elements. Also, while anumber of particular embodiments have been set forth, it will beunderstood that features and aspects that have been described withreference to each particular embodiment can be used with each remainingparticularly set forth embodiment. For example, features or aspectsdescribed with respect to FIG. 3 can be used, combined with or replacefeatures described using FIGS. 4-6.

1. A refrigerant vapor compression system comprising: a refrigerantcompression device to include a first compression stage and a secondcompression stage; a refrigerant heat rejection heat exchangerdownstream of said compression device; a refrigerant heat absorptionheat exchanger downstream of said refrigerant heat rejection heatexchanger; a first expansion device disposed downstream of saidrefrigerant heat rejection heat exchanger and upstream of saidrefrigerant heat absorption heat exchanger; a sensor coupled to anoutput of the heat rejection heat exchanger, the sensor to measure arefrigerant temperature; and a controller to control operations of therefrigeration vapor compression system, said controller operative toindirectly verify the measured refrigerant temperature.
 2. Therefrigerant vapor compression system of claim 1, where the refrigeranttemperatures at the output of the heat rejection heat exchanger is firstdetermined by measurement using the sensor, wherein the refrigeranttemperature is second determined by calculation using ambienttemperature and vapor pressure system capacity.
 3. The refrigerant vaporcompression system of claim 2, where a vapor compression system capacityhas a prescribed relationship with an operating mode or differencebetween supply air temperature and return air temperature; and whereinan offset is added to the ambient temperature responsive to the vaporcompression system capacity.
 4. The refrigerant vapor compression systemof claim 3, the controller to operate the vapor compression system withthe calculated value for the refrigerant temperature when the measuredrefrigerant temperature is different from the calculated temperaturevalue.
 5. The vapor compression system of claim 1, where said sensor isa pressure sensor or a temperature sensor.
 6. The refrigerant vaporcompression system of claim 1, comprising a second sensor to measure acompressor mid stage pressure, said controller to indirectly verify saidmeasured compressor mid stage pressure.
 7. The refrigerant vaporcompression system of claim 6, where the compressor mid stage pressureis calculated using a discharge pressure and an inlet pressure of thecompressor.
 8. The refrigerant vapor compression system of claim 7,wherein the controller to operate the vapor compression system using theverified value of the compressor mid stage pressure where the measuredcompressor mid stage pressure does not match the indirectly verifiedvalue.
 9. The refrigerant vapor compression system of claim 8,comprising: a second valve disposed downstream of the heat rejectionheat exchanger; and an economizer circuit disposed downstream of thesecond valve and upstream of the first expansion device, the economizercircuit including a refrigerant injection line to open to anintermediate pressure stage of the compression device and a flow controlvalve disposed in the refrigerant injection line.
 10. The refrigerantvapor compression system of claim 9, said controller to close the flowcontrol valve when the compressor mid-stage pressure is operative tocause refrigerant flow toward the economizer circuit.
 11. Therefrigerant vapor compression system of claim 1, comprising: a flashtank economizer disposed in serial flow relationship between the heatrejection heat exchanger and the first expansion device, said flash tankeconomizer including: a flash tank; a first flow control device disposedbetween the heat rejection heat exchanger and said flash tank; aneconomizer vapor line to fluidly interconnect said flash tank to amid-stage of the compressor; and a second flow control device disposedin said economizer vapor line.
 12. A method for determining acharacteristic of a refrigerant vapor compression system having arefrigerant circuit including a refrigerant compression device, arefrigerant heat rejection heat exchanger downstream of said compressiondevice, a refrigerant heat absorption heat exchanger downstream of saidrefrigerant heat rejection heat exchanger, a sensor to sense acharacteristic used to determine a system capacity of the refrigerantvapor compression system during operation, and interconnectingrefrigerant lines as active components, the method comprising: operatingthe refrigerant vapor compression system in a mode where the refrigerantis circulating within the active components of the refrigerant circuit;indirectly determining said characteristic used to determine the systemcapacity; comparing the sensed value of said characteristic used todetermine the system capacity against said indirectly determined valueof said characteristic; and determining an error condition of acorresponding sensor when a result of the comparison does not match. 13.The method of claim 12, comprising subsequently using the indirectlydetermined value in operating the vapor compression system.
 14. Themethod of claim 13, wherein said characteristic to determine systemcapacity is a refrigerant temperature at an output of the heat rejectionheat exchanger.
 15. A computer program product comprising a computerusable storage medium to store a computer readable program that, whenexecuted on a computer, causes the computer to perform operations tooperate a transport refrigeration unit, the operations comprising:operating the transport refrigeration unit in a mode where a refrigerantis circulating within a refrigerant circuit; sensing a characteristicused to determine a system capacity of the transport refrigeration unitduring operation; indirectly determining said characteristic used todetermine the system capacity; comparing the sensed value of the saidcharacteristic used to determine the system capacity against saidindirectly determined value; and determining an error condition of acorresponding sensor when a result of the comparison does not match.